As this theory goes, our bodies take in less oxygen because our breathing has slowed. Therefore, yawning helps us bring more oxygen into the blood and move more carbon dioxide out of the blood. ... Stretching and yawning may be a way to flex muscles and joints, increase heart rate, and feel more awake.

What is the main cause of yawning?

Yawning is a mostly involuntary process of opening the mouth and breathing in deeply, filling the lungs with air. It's a very natural response to being tired. In fact, yawning is usually triggered by sleepiness or fatigue. Some yawns are short, and some last for several seconds before an open-mouthed exhale.

Is yawning due to a lack of oxygen?

This seems logical since yawning does bring in more oxygen with a deep breath and the expiration removes more carbon dioxide than the usual breath, but research by putting people in low-oxygen or high- carbon-dioxide environments does not cause yawning.